In general, a color reproduction range (color gamut) of display devices, printing devices, image pickup devices, and the like is different by the model. In addition, for color television apparatuses, the color reproduction range of inputted video signals is different by the employed television system. For this reason, conventionally, when generating output data based on inputted data, color conversion processing of a variety of types has been performed in order to output color as accurately as possible to inputted data regardless of differences in the color reproduction range. For example, when performing HDTV (High Definition Television) broadcasting using a color television apparatus that employs a liquid crystal panel, signals in a standard specified by ITU-R (International Telecommunication Union Radiocommunications Sector) BT.709 (hereinafter referred to as the “HDTV standard”) are supplied to the color television apparatus from an external signal source. In this case, the signals supplied to the color television apparatus from the external signal source are RGB signals. In the color television apparatus, mapping (matching) processing of a color gamut of the RGB signals supplied from the signal source to a color gamut in the liquid crystal panel that constitutes the color television apparatus (hereinafter referred to as the “color gamut conversion processing”) is performed. Then, voltages corresponding to values of colors included in the RGB signals obtained through the color gamut conversion processing are applied to the liquid crystal layer. With this, colors are displayed in a display unit of the liquid crystal panel as accurately as possible to colors represented by the RGB signals supplied from the signal source. The following describes such color gamut conversion processing performed in the color television apparatus in detail.
FIG. 14 is a table for showing chromaticity coordinate values of primary colors (coordinate values in an xy chromaticity diagram) in the HDTV standard and chromaticity coordinate values of primary colors of one liquid crystal panel that constitutes a display device (color television apparatus). Referring to FIG. 14, for example, it can be seen that “the value of the chromaticity coordinate (x, y) for R (red) is (0.6400, 0.3300) in the HDTV standard”. In this case, by performing normalization so that brightness Y of W (white) in the XYZ color space is 1 based on information related to the HDTV standard represented by a reference numeral 91 in FIG. 14, a following equation (1) expressing a relation between the RGB values and the XYZ values can be obtained. Here, X, Y, and Z are tristimulus values in an XYZ colorimetric system.
                              (                                                    X                                                                    Y                                                                    Z                                              )                =                              (                                                                                0.4124                    ,                                                                                        0.3576                    ,                                                                    0.1805                                                                                                  0.2126                    ,                                                                                        0.7152                    ,                                                                    0.0722                                                                                                  0.0913                    ,                                                                                        0.1192                    ,                                                                    0.9505                                                      )                    ⁢                                    (                                                                    R                                                                                        G                                                                                        B                                                              )                        in                                              (        1        )            
Similarly, based on information related to the liquid crystal panel represented by a reference numeral 92 in FIG. 14, a following equation (2) expressing a relation between the RGB values and the XYZ values can be obtained.
                              (                                                    X                                                                    Y                                                                    Z                                              )                =                              (                                                                                0.4091                    ,                                                                                        0.3101                    ,                                                                    0.2840                                                                                                  0.2071                    ,                                                                                        0.6906                    ,                                                                    0.1023                                                                                                  0.0136                    ,                                                                                        0.0913                    ,                                                                    0.5085                                                      )                    ⁢                                    (                                                                    R                                                                                        G                                                                                        B                                                              )                        out                                              (        2        )            
Furthermore, where “right side in the equation (1)=the right side in the equation (2)”, a following equation (3) can be obtained.
                                          (                                                            R                                                                              G                                                                              B                                                      )                    out                =                              (                                                                                1.0002                    ,                                                                                        0.1021                    ,                                                                                        -                    0.0056                                                                                                                    0.0075                    ,                                                                                        0.0024                    ,                                                                    0.0130                                                                                                  0.0033                    ,                                                                                        0.0174                    ,                                                                    0.6294                                                      )                    ⁢                                    (                                                                    R                                                                                        B                                                                                        G                                                              )                        in                                              (        3        )            
In this case, the equation (3) is to obtain the values of the respective RGB colors corresponding to values of voltage to be applied to a liquid crystal layer in the liquid crystal panel based on the RGB signals in the HDTV standard supplied from the signal source. Specifically, as shown in FIG. 15, an RGB signal RGBin in the HDTV standard is inputted to a display device (color television apparatus) 9 from a signal source 93, and the RGB signal RGBin is converted based on the equation (3) by a color gamut conversion processing unit 94. Then, an RGB signal RGBout obtained through the conversion processing by the color gamut conversion processing unit 94 is supplied to a liquid crystal panel 95. In this manner, colors accurate to colors represented by the RGB signal RGBin supplied from the signal source 93 are displayed in a display unit of the liquid crystal panel 95.
In relation to the present invention, the following prior art documents are known. Japanese Unexamined Patent Application Publication No. H04-291591 discloses an invention relating to a color display device capable of reproducing colors of any of inputted video signals having different color reproduction ranges from each other without a color reproduction error. Japanese Unexamined Patent Application Publication No. 2008-78737 discloses a technique of preventing waste of a color gamut of an image output device by correcting brightness or luminance. Japanese Unexamined Patent Application Publication No. 2008-86029 discloses a method of acquiring desired color reproduction by utilizing a standard color space with an extended color gamut.